In automobile engines, it is necessary to provide a drive means capable of transmitting rotational drive from the engine crank shaft to the cam shaft. It is preferable that this drive means also allows the phase of the cam, that is the relationship between the rotational orientation of the crank shaft and the rotational orientation of the cam shaft, to be varied whilst the engine is running. Currently available variable cam phasers typically employ a mechanical actuator comprising a planetary gearset and worm gear drive. In order to vary the cam phase a sun gear of the planetary gearset is rotated by a DC motor; this causes the planet gears to rotate around the sun gear thereby adjusting the rotational orientation of the cam shaft. However, such systems rely on a high degree of physical contact between the gears in order to operate; this can create a large amount of friction and noise between the gears, thereby leading to inefficiency in the conversion process. This is particularly problematic under the high loads experienced in an automobile engine.
A currently available solution to this is to use an oil-based hydraulic cam phaser; however, these are susceptible to poor performance at extremes of temperature and at low engine speeds.